Abstract
Objective To investigate genetic characteristics of Neisseria gonorrhoeae (N. gonorrhoeae)isolates from Guangzhou city in 2014, and to analyze the relationship of N. gonorrhoeae multi-antigen sequence typing (NG-MAST)sequence types(STs)with ciprofloxacin resistance. Methods An agar dilution method was used to determine the minimal inhibitory concentration(MIC)of ciprofloxacin in 97 N. gonorrhoeae isolates from Guangzhou city. PCR was performed to amplify the gyrA, parC, porB and tbpB genes from these isolates, followed by gene sequencing and determination of NG-MAST STs. Results Of the 97 N. gonorrhoeae isolates, 95 (97.9%)were resistant to ciprofloxacin, including 41 high-level (MIC ≥ 16 mg/L)and 54 low-level (1 mg/L ≤ MIC < 16 mg/L)resistant strains. Mutations were detected at codons 91 and 95 encoding serine in the gyrA gene of all the 95 ciprofloxacinresistant strains, and in the parC gene of 93 resistant strains. The frequency of the mutation at codon 87 in the parC gene was 85.4% (35/41)in high-level resistant strains, significantly higher than that in low-level resistant strains (59.3%[32/54], χ2 = 7.64, P < 0.05). MAST STs were successfully determined for all the 97 N. gonorrhoeae isolates except 1 isolate with incorrect PCR amplicons. Of the 96 genotyped isolates, 50 were assigned to 35 known STs by using the NG-MAST website (www. ng-mast.net), among which, 10 STs each contained 2 to 4 isolates. The most common ST was ST5309. Phylogenetic tree analysis revealed that the 96 genotyped N. gonorrhoeae isolates could be classified into 2 groups, and the proportion of isolates with MIC ≥ 16 mg/L is 46.4% (39/84)in group 1, but only 1/12 in group 2 (χ2 = 6.27, P = 0.012). Conclusions High-level resistance of N. gonorrhoeae to ciprofloxacin may be mainly associated with the mutation at codon 87 in the parC gene. NG-MAST STs may be related to the degree of ciprofloxacin resistance. Key words: Neisseria gonorrhoeae; Ciprofloxacin; Drug resistance, bacterial; NG-MAST
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